The present invention relates to a light-sensitive silver halide emulsion, and more particularly to a method for producing stably a monodisperse silver halide emulsion which, after being chemically sensitized, has little fog, a high sensitivity and excellent graininess.
In recent years there have been growing even severe demands for photographic silver halide emulsions; particularly still higher level of demands have been arising for such photographic characteristics as higher sensitivity, more excellent graininess, higher sharpness, lower fog density, more sufficiently high density, and the like.
As a high sensitivity-having emulsion that can meet such demands there is well-known a silver iodobromide emulsion containing from 0 to 10 mole % of iodine. As the method for preparing such an emulsion there are conventionally known such methods using pH or pAg condition control as the ammoniacal method, neutral method, acid method and the like, and such mixing methods as the single jet method, double jet method and the like. On the basis of these known techniques, high level of technical means have been studied and made practical reality for the purpose of attaining further high sensitization, improvement on graininess, excellent sharpness and reduction of fog. In regard to the silver iodobromide emulsion which is the subject of the present invention, studies have been made to produce an emulsion whose crystal habit, granularity distribution, and further the concentration distribution of iodine inside individual silver halide particles are controlled.
The most orthodox method for attaining the above-mentioned photographic characteristics such as high sensitivity, excellent graininess, high sharpness, less fog density, sufficiently high covering power and the like is to improve the quantum efficiency of the silver halide. For this purpose, the knowledge of solid-state physics is positively introduced into it. The study in which the quantum efficiency is theoretically calculated to contemplate the influence thereof upon the granularity distribution is described, e.g., on page 91 of the paper entitled the "Interactions between Light and Materials for Photographic Applications" prepared for the Tokyo Symposium 1980 for the Advancement of Photography. This study predicts that the preparation of a monodisperse emulsion with its granularity distribution narrowed down is effective for the improvement of the quantum efficiency. In addition to this, there is considered reasonable the inference in the study that the monodisperse emulsion would be advantageous also for attaining effectively the high sensitization with keeping the emulsion on a less fog level in the process called chemical sensitization that will be detailed hereinafter.
In order to produce a monodisperse emulsion industrially as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 48521/1979, there are required the supply speed controls of silver and halide ions in the theoretical amounts each to the reaction system under rigid pAg and pH controls and a sufficient condition of stirring the system.
And it is also known that the configuration of the silver halide particle is made differently according to the pAg during the growth of the silver halide particle. The silver halide emulsion prepared under these conditions is in any one of the regular hexahedral, octahedral and tetradecahedral crystal forms each comprising the so-called regular crystal particles consisting in various proportions of the (100) face to (111) face.
The measurement and control of pAg are monitored to be carried out by the use of apparatus known to those skilled in the art. Typical and effective control apparatus is as described in U.S. Pat. No.3,031,304 and Photographische Korrespondenz vol. 103, pp. 161-164 (1967).
Japanese Patent Examined Publication No.23443/1973 shows that the emulsion of cubic crystal particles comprised of the (100) face prepared under a low pAg condition has fog increased. by a chemical sensitization, and on the other hand, the emulsion of octahedral crystal particles comprised of the (111) face prepared under a high pAg condition has photographically desirable characteristics. However, any negative-type highly sensitive emulsion comprising octahedral silver iodobromide crystal particles is still not made practical reality. It is mainly because of the difficulty in the manufacture of silver halide emulsions comprising a group of monodisperse octahedral crystal particles. The foregoing Japanese Patent Examined Publication No. 23443/1973 suggests that a satisfactory mono dispersibility-having octahedral emulsion can be obtained by changing pAg during the preparation of silver halide particles. However, as it is understood from the report in the Journal of Photographic Science vol. 27, p. 47-53 (1979), even if the pAg were changed in two stages, satisfactory monodispersibility-having octahedral particles could be obtained only in a very limited pAg range. Besides, what is described in the report relates to pure silver bromide, and in such a silver iodobromide or silver iodochloride emulsion as containing a few mole % of iodine it is further difficult to prepare an emulsion compris a group of monodisperse octahedral particles, so that any practically usable emulsion comprising a group of monodisperse octahedral particles has conventionally been unable to be obtained stably.
One reason of the above is that the accuracy of the pAg control in the potential difference measurement is up to the pAg value range of .+-.0.1, and another is that, in the case of silver iodobromide or silver iodochloride emulsion, with an increase in the silver iodide content percentage, the production of twin and new fine particles becomes increased.
An ideal silver halide emulsion requires the conditions that the particle sizes thereof from a normal distribution whose width is small and the particle's configurations are well uniform. In those conventionally known techniques, the emulsion whose particle size distribution is small and the method for the production thereof are known, and an emulsion comprising regular cubic crystal particles is relatively easier to produce, but in the octahedral or tetradecahedral emulsion, the frequency of twinning was considerably high. In twin particles, generally, their growth rate is high and they tend to become coarse grained, so that the frequency thereof in the number is small but the overally volume thereof occupying the entirety is very large, thus significantly affecting the photographic characteristics. And because twin is capable of taking various configurations, the charactors thereof to the chemical sensitization are largely diversified. Some of them appear as fog even under a relatively weak sensitization condition, and some are hardly sensitive, the so-called dead grain, even under a strong sensitization condition, which causes bad efficiency.
Even useful twin particles that are sensitive to light and normally developable, due to the size thereof, invites undesirably the deterioration of the graininess.